Fix omp update directive in trgtol_mod (no MPI code path)

[thomasgibson]

This is a very minor PR correcting an OMP directive when building ECTrans without MPI, for PR #211

I used the test program from @samhatfield's comment here to verify the OMP implementation on the GPU on MI300A with and without unified memory enabled. I am getting identical results in both cases!

Here are the results running on MI300A in "discrete GPU" mode (HSA_XNACK=0):
single precision:

ecTrans at version: 1.5.1
commit: 59c7ff9739dac8e1332f7c788dbbe3f67a929eb1

 R%NTMAX= 79
 R%NSMAX= 79
 setup_trans: sizes1 NUMP= 80
 Using OpenMP offloading
    FG%ZAS:       611840B
    FG%ZAA:       611840B
   FG%ZAS0:        26240B
   FG%ZAA0:        25600B
 FG%ZEPSNM:        26240B
 ===GPU arrays successfully allocated
 GRID_POINT_FIELD =  -3.66075754,  3.66075754
 TEST_PROGRAM 1
 Error =  2.612723335E-7

double precision:

ecTrans at version: 1.5.1
commit: 59c7ff9739dac8e1332f7c788dbbe3f67a929eb1

 R%NTMAX= 79
 R%NSMAX= 79
 setup_trans: sizes1 NUMP= 80
 Using OpenMP offloading
    FG%ZAS:      1223680B
    FG%ZAA:      1223680B
   FG%ZAS0:        26240B
   FG%ZAA0:        25600B
 FG%ZEPSNM:        52480B
 ===GPU arrays successfully allocated
 GRID_POINT_FIELD =  -3.6607575710598272,  3.6607575710598272
 TEST_PROGRAM 1
 Error =  8.00660226648715344E-15

With unified memory enabled (HSA_XNACK=1):
single precision:

ecTrans at version: 1.5.1
commit: 59c7ff9739dac8e1332f7c788dbbe3f67a929eb1

 R%NTMAX= 79
 R%NSMAX= 79
 setup_trans: sizes1 NUMP= 80
 Using OpenMP offloading
    FG%ZAS:       611840B
    FG%ZAA:       611840B
   FG%ZAS0:        26240B
   FG%ZAA0:        25600B
 FG%ZEPSNM:        26240B
 ===GPU arrays successfully allocated
 GRID_POINT_FIELD =  -3.66075754,  3.66075754
 TEST_PROGRAM 1
 Error =  2.612723335E-7

double precision:

ecTrans at version: 1.5.1
commit: 59c7ff9739dac8e1332f7c788dbbe3f67a929eb1

 R%NTMAX= 79
 R%NSMAX= 79
 setup_trans: sizes1 NUMP= 80
 Using OpenMP offloading
    FG%ZAS:      1223680B
    FG%ZAA:      1223680B
   FG%ZAS0:        26240B
   FG%ZAA0:        25600B
 FG%ZEPSNM:        52480B
 ===GPU arrays successfully allocated
 GRID_POINT_FIELD =  -3.6607575710598272,  3.6607575710598272
 TEST_PROGRAM 1
 Error =  8.00660226648715344E-15