drivers: counter: Fix redundant identical condition

There was an unnecessary nested `if` in `ifx_cat1_counter_init` with the
same condition already checked in the outer block.

This results in dead and redundant code with no functional impact but
harms readability.

The inner `if (rslt != CY_RSLT_SUCCESS)` was removed to clean up the
function.

Signed-off-by: Gaetan Perrot <gaetan.perrot@spacecubics.com>