spi: lm70llp: remove printk

Using pr_* macros are more prefferable than using printk. Start using
pr_* family of macros and define pr_fmt to be used with it.
While at it remove DRVNAME from an existing pr_info() as the name is now
being printed by pr_fmt.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Mark Brown <broonie@kernel.org>