fix conflicting types

[stronnag]

gcc 13.1.1 reports a (mainly harmless) conflicting type:

/src/main/drivers/flash.c:221:19: warning: conflicting types for 'flashPartitionFindByType' due to enum/integer mismatch; have 'flashPartition_t *(uint8_t)' {aka 'struct flashPartition_s *(unsigned char)'} [-Wenum-int-mismatch]
  221 | flashPartition_t *flashPartitionFindByType(uint8_t type)
      |                   ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from ./src/main/drivers/flash.c:31:
./src/main/drivers/flash.h:101:19: note: previous declaration of 'flashPartitionFindByType' with type 'flashPartition_t *(flashPartitionType_e)' {aka 'struct flashPartition_s *(flashPartitionType_e)'}
  101 | flashPartition_t *flashPartitionFindByType(flashPartitionType_e type);
      |  

So let's fix it ...