ddr: altera: Trivial mem_calibrate() indent cleanup

ddr: altera: Trivial mem_calibrate() indent cleanup

Redo the mega-condition such that if the calibration is to be skipped,
the positive branch of the condition does all the work and returns.
The negative branch, which is in fact the default behavior, is then
converted to a code which is no longer conditional. This trims down
the indent by one level.

Signed-off-by: Marek Vasut <marex@denx.de>