Despite its name, commit fed74d75 ("pinctrl: mediatek: common-v2:
Fix bias-disable for PULL_PU_PD_RSEL_TYPE") actually broke bias-disable
for PULL_PU_PD_RSEL_TYPE.

mtk_pinconf_bias_set_combo() tries every bias method supported by the
pin until one succeeds. For PULL_PU_PD_RSEL_TYPE pins, before the
breaking commit, mtk_pinconf_bias_set_rsel() would be called first to
try and set the RSEL value (as well as PU and PD), and if that failed,
the only other valid option was that bias-disable was specified, which
would then be handled by calling mtk_pinconf_bias_set_pu_pd() and
disabling both PU and PD.

The breaking commit misunderstood this logic and added an early "return
0" in mtk_pinconf_bias_set_rsel(). The result was that in the
bias-disable case, the bias was left unchanged, since by returning
success, mtk_pinconf_bias_set_combo() no longer tried calling
mtk_pinconf_bias_set_pu_pd() to disable the bias.

Since the logic for configuring bias-disable on PULL_PU_PD_RSEL_TYPE
pins required mtk_pinconf_bias_set_rsel() to fail first, in that case,
an error was printed to the log, eg:

  mt8195-pinctrl 10005000.pinctrl: Not support rsel value 0 Ohm for pin = 29 (GPIO29)

This is what the breaking commit actually got rid of, and likely part of
the reason why that commit was thought to be fixing functionality, while
in reality it was breaking it.

Instead of simply reverting that commit, restore the functionality but
in a way that avoids the error from being printed and makes the code
less confusing:
* Return 0 explicitly if a bias method was successful
* Introduce an extra function mtk_pinconf_bias_set_pu_pd_rsel() that
  calls both mtk_pinconf_bias_set_rsel() (only if needed) and
  mtk_pinconf_bias_set_pu_pd()
  * And analogously for the corresponding getters

Fixes: fed74d75 ("pinctrl: mediatek: common-v2: Fix bias-disable for PULL_PU_PD_RSEL_TYPE")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/20240808-mtk-rsel-bias-disable-fix-v1-1-1b4e85bf596c@collabora.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>