The code in the BRCM80211 BRCMSMAC driver is using the legacy
GPIO API to to a complex check of the validity of the base of
the GPIO chip and whether it is present at all and then adding
an offset to the base of the chip.

Use the existing function to obtain a GPIO line internally
from a GPIO chip so we can use the offset directly and
modernize the code to use GPIO descriptors instead of integers
from the global GPIO numberspace.

Cc: Wright Feng <wright.feng@cypress.com>
Cc: Frank Kao <frank.kao@cypress.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200711210150.4943-1-linus.walleij@linaro.org