ddr: altera: Repair uninited variable

ddr: altera: Repair uninited variable

Fix the following problem:
drivers/ddr/altera/sequencer.c: In function 'sdram_calibration_full':
drivers/ddr/altera/sequencer.c:1943:25: warning: 'found_failing_read' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (found_passing_read && found_failing_read)
                         ^
drivers/ddr/altera/sequencer.c:1803:26: note: 'found_failing_read' was declared here
  u32 found_passing_read, found_failing_read, initial_failing_dtap;
                          ^

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