driver: sensor: adxl372: Bug fix for status2 reg

This is a bug fix for adxl372_get_status function.
This function is used to get STATUS1, STATUS2, FIFO_ENTRIES2
and FIFO_ENTRIES1 registers (they are continuously present
in the memory in this order). User can choose if it wants
STATUS2 and/or FIFO registers by passing pointers where
to store received values. Bug was when user doesn't want
STATUS2 and want FIFO regs. In that case calculated length
would be 3 which will result in reading of STATUS1, STATUS2
and FIFO_ENTRIES2 regs and not expected STATUS1, FIFO_ENTRIES2
and FIFO_ENTRIES1.

Signed-off-by: Vladislav Pejic <vladislav.pejic@orioninc.com>