misc: sram: Improve and simplify clk handling

misc: sram: Improve and simplify clk handling

The current code tries to get an associated clk, ignores any errors in the
process and if there is a clock enables it unconditionally for the whole
lifetime of the sram device.

Instead use an "optional" variant of devm_clk_get() which handles the case
where no clk is needed for the sram device and do proper error handling
for the remaining error cases. Also use an "enabled" variant of
devm_clk_get() to simplify. With that .probe() is the only function using
struct sram_dev::clk, so it can be replaced by a local variable.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20230302091251.1852454-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>