ARM: dts: msm8974-FP2: Increase load on l20 for sdhci

Before this change, trying to boot from the internal storage would
result in a lot of errors like:

[   11.224046] mmc0: cache flush error -110
[   11.224180] blk_update_request: I/O error, dev mmcblk0, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0

or:

[  137.544673] mmc0: tuning execution failed: -5
[  137.569832] mmcblk0: error -110 requesting status
[  137.593558] mmcblk0: recovery failed!

With this patch, there are no more sdhci errors and booting works fine.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>