pwm: lp3943: Fix potential memory leak during request

Fix a memory leak in the lp3943_pwm_request_map() error handling path.
Make sure already allocated pwm map memory is freed correctly.
Detected by Coverity: CID 1162829.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Acked-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>