Input: himax_hx83112b - fix incorrect size when reading product ID

We need to read a u32 value (4 bytes), not size of a pointer to that
value.

Also, himax_read_mcu() wrapper is an overkill, remove it and use
himax_bus_read() directly.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202408200301.Ujpj7Vov-lkp@intel.com/


Fixes: 0944829d ("Input: himax_hx83112b - implement MCU register reading")
Tested-by: Felix Kaechele <felix@kaechele.ca>
Link: https://lore.kernel.org/r/ZsPdmtfC54R7JVxR@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>