create_inode: fix gcc -Wall warnings #76

Job	Run time
Build and test with gcc	57s
Build and test with clang	1m 36s
Build and test with ASAN enabled	1m 31s
Cross-compile for Android (aarch64)	44s
Cross-compile for Android (armv7a)	39s
Build and test with gcc -m32	1m 13s
Build and test on macOS	2m 29s
Cross-compile for Android (i686)	39s
Build and test with UBSAN enabled	1m 24s
Cross-compile for Android (x86_64)	42s
Build mke2fs on Windows with mingw32	2m 23s
Build mke2fs on Windows with mingw64	2m 17s
	16m 34s

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