spi: omap2-mcspi: Fix the IS_ERR() bug for devm_clk_get_optional_enabled()

The devm_clk_get_optional_enabled() function returns error
pointers(PTR_ERR()). So use IS_ERR() to check it.

Verified on K3-J7200 EVM board, without clock node mentioned
in the device tree.

Signed-off-by: Purushothama Siddaiah <psiddaiah@mvista.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Link: https://patch.msgid.link/20241205070426.1861048-1-psiddaiah@mvista.com


Signed-off-by: Mark Brown <broonie@kernel.org>