firmware: arm_scmi: Avoid non-constant printk format strings

firmware: arm_scmi: Avoid non-constant printk format strings

A recent rework changed the constant format strings to a local variable,
which causes warnings from clang when -Wformat-security is enabled:

drivers/firmware/arm_scmi/driver.c: In function 'scmi_probe':
drivers/firmware/arm_scmi/driver.c:2936:25: error: format not a string literal and no format arguments [-Werror=format-security]
 2936 |                         dev_err(dev, err_str);
      |                         ^~~~~~~
drivers/firmware/arm_scmi/driver.c:2993:9: error: format not a string literal and no format arguments [-Werror=format-security]
 2993 |         return dev_err_probe(dev, ret, err_str);

Print these using an explicit "%s" string instead.

Fixes: 3a7d93d1f71b ("firmware: arm_scmi: Use dev_err_probe to bail out")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240403111040.3924658-1-arnd@kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>