phy: ti: am654: simplify return handling

Checking return value after each regfield write becomes
hard to read quickly as number of writes increase.

Simplify by checking for error only once.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Link: https://lore.kernel.org/r/20200727194603.44636-3-nsekhar@ti.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>