Scripts/runpft: eleminate the warning message 'line 163: [[: NN: value too great for base (error token is NN)'

Add dummay char to the memsize test, to eleminate the warning message
        "line 163: [[: NN: value too great for base (error token is NN)"
,where NN is the value specified by PFT_MEMSIZE.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>