Change rtic-tick example system clock to fix assert.

[linuxtim]

The rtic-tick example asserts during clock setup because the code attempts to configure a clock of 8 MHz, which is below the lowest SYSCLK_MIN defined in src/rcc/mod.rs (12.5 MHz). Change requested clock to 48 MHz (above the highest SYSCLK_MIN of 24 MHz).

[burrbull]

Add link on PR to changelog:

stm32f4xx-hal/CHANGELOG.md

Line 14 in 6f42b2c

- Implementation of RTIC Monotonic for TIM2 & TIM5 under `rtic` feature [#380]

[linuxtim]

Add link on PR to changelog

My thought was that since the fixed code was unreleased, the additional noise it would generate wouldn't justify a changelog entry. I've pushed a minimal change. Please feel free to edit the revised commit if it's unsatisfactory.

[burrbull]

bors r+

[bors]

Build succeeded:

• ci (stm32f401, stable)
• ci (stm32f405, stable)
• ci (stm32f407, stable)
• ci (stm32f410, stable)
• ci (stm32f411, stable)
• ci (stm32f412, stable)
• ci (stm32f413, stable)
• ci (stm32f415, stable)
• ci (stm32f417, stable)
• ci (stm32f423, stable)
• ci (stm32f427, stable)
• ci (stm32f429, stable)
• ci (stm32f437, stable)
• ci (stm32f439, stable)
• ci (stm32f446, stable)
• ci (stm32f469, stable)
• ci (stm32f479, stable)
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