fix a typo in Documentation/pi-futex.txt
fix a typo in Documentation/pi-futex.txt

Signed-off-by: Riccardo Magliocchetti <ff4b963c478aa826155878455ec58bfb9570caee@datahost.it>
Signed-off-by: Adrian Bunk <0b86548ef377da0031a3ff3f0c4e06f016e20105@stusta.de>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas