pinctrl: single: Fix pcs_parse_bits_in_pinctrl_entry to use __ffs than ffs

pcs_parse_bits_in_pinctrl_entry uses ffs which gives bit indices
ranging from 1 to MAX. This leads to a corner case where we try to request
the pin number = MAX and fails.

bit_pos value is being calculted using ffs. pin_num_from_lsb uses
bit_pos value. pins array is populated with:

pin + pin_num_from_lsb.

The above is 1 more than usual bit indices as bit_pos uses ffs to compute
first set bit. Hence the last of the pins array is populated with the MAX
value and not MAX - 1 which causes error when we call pin_request.

mask_pos is rightly calculated as ((pcs->fmask) << (bit_pos - 1))
Consequently val_pos and submask are correct.

Hence use __ffs which gives (ffs(x) - 1) as the first bit set.

fixes: 4e7e8017 ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
Signed-off-by: Keerthy <j-keerthy@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>